The present invention relates to a mounting structure of a bumper beam on at least one of the front and rear sides of a vehicle.
At lower parts on the front side and rear side of a vehicle, bumpers are provided. Bumpers protect functional parts such as the body and lamps of a vehicle when the vehicle collides with other objects. At the back of a bumper, a bumper beam is provided to absorb shock energy when the vehicle body receives a shock in a collision.
Bumpers come in various shapes depending on the size of the vehicle. Furthermore, because bumpers also play a role in enhancing design properties, bumpers have a variety of different design shapes used in accordance with the vehicle type. Therefore, many types of bumper beams have been manufactured so as to match the bumper shape.
To manufacture a bumper beam, a material such as a steel sheet is used. The steel sheet used for the bumper beam has a thickness larger than a predetermined thickness to ensure the strength of the whole bumper beam. The bumper beam is manufactured by being integrally molded so as to match the length in the vehicle width direction by means of roll molding or press molding.
A bumper beam structure is disclosed in, for example, Japanese Patent Provisional Publication No. 2000-85496. In this vehicular bumper device, a recessed part is provided in the front surface of a bumper reinforce member, and one pipe-shaped reinforcing matter is attached to this recessed part so as to be fitted in the recessed part.
Further, Japanese Utility Model Publication No. 5-27315 discloses a bumper structure in which a pair of upper and lower reinforce members formed of a steel pipe are arranged at an upper part of a side frame.
However, in order to manufacture bumper beams having different shapes and sizes depending on the vehicle type and model, many kinds of press molding dies are needed to fabricate steel sheets. Also, in order to integrally press mold the bumper beam over the total length in the width direction of vehicle, a large molding die is needed, and further the manufacturing equipment is also increased in size. This requires high manufacturing cost and managing expense for the dies, so that it is not easy to reduce the manufacturing cost of vehicle as a whole.
Also, in order to decrease the weight of a bumper beam, it is necessary to decrease the material thickness thereof. However, a decrease in material thickness lowers the bending strength of the whole of the bumper beam. Therefore, there is a limit in achieving decreased weight and increased strength of the bumper beam at the same time.
On the other hand, in the structure described in Japanese Patent Provisional Publication No. 2000-85496, since the reinforcing matter is formed by only one pipe, shock energy is absorbed insufficiently.
Also, in the structure described in Japanese Utility Model Publication No. 5-27315, since the reinforce members are provided at the upper part of the side frame, for example, when a force is applied to the reinforce member from the outside of vehicle, the force is received only by the strength of the reinforcing members. To compensate for that, the steel pipe forming the reinforcing member is increased in size.